The Internet of things (The Internet of Things) refers to: Obtain information about a physical world by deploying various devices having perception, calculation, execution, and communication capabilities, and implement information transmission, orchestration, and processing by using a network, to further implement a network interconnecting people and things and interconnecting things. With continuous development of the Internet of things technologies, research on how to bear an application of the Internet of things by using a mobile communications network has been started currently. In this research, to reduce device costs and satisfy a requirement for low consumption, an operating bandwidth of a device needs to be reduced. For example, bandwidths of a radio frequency and a baseband of the device are reduced to 1.4 MHz. User equipment whose operating bandwidth is reduced is referred to as narrowband user equipment.
According to an existing protocol, a base station in a communications system transmit scheduling information to user equipment by using a PDCCH (Physical Downlink Control Channel) or an EPDCCH (Enhanced Physical Downlink Control Channel). The scheduling information is used to indicate a transmission manner of to-be-transmitted data, for example, a used time frequency resource, or a used modulation and coding scheme. In the EPDCCH channel, a CSS (Common Search Space) used to schedule a common message is not defined, and only a USS (UE specific Search Space) used to schedule user specific data is defined. In addition, configuration information of the USS that is defined in the EPDCCH and that is used to schedule user specific data is transmitted by using RRC (Radio Resource Control) signaling scheduled by using a PDCCH.
However, if a system bandwidth is greater than an operating bandwidth of narrowband user equipment, the narrowband user equipment cannot receive a PDCCH channel of a system because the PDCCH channel may be mapped and distributed through a range of the entire system bandwidth. Furthermore, the narrowband user equipment cannot receive the configuration information of the USS in the EPDCCH by receiving the RRC signaling according to the existing protocol, and cannot configure the USS in the EPDCCH. Consequently, no physical downlink control channel is available for the narrowband user equipment, and data cannot be scheduled or transmitted.
Therefore, for a scenario in which a system bandwidth is greater than an operating bandwidth of narrowband user equipment, how to transmit a physical downlink control channel is a problem urgently to be resolved.